Use this procedure to troubleshoot suspect problems with the circuit for the turbocharger compressor bypass system.
This procedure covers the following diagnostic codes:
- 1720-9 Turbocharger Compressor Bypass Valve Actuator : Abnormal Update Rate
- 1720-11 Turbocharger Compressor Bypass Valve Actuator invalid
- 1720-12 Turbocharger Compressor Bypass Valve Actuator : Failure
These codes indicate an abnormal operating condition in the turbocharger compressor bypass valve actuator. Refer to literature from the OEM for troubleshooting the turbocharger compressor bypass valve actuator.
A bypass valve is connected between the outlets for the turbocharger compressors and the inlets for the turbocharger compressors. The bypass valve is activated by an actuator. The Electronic Control Module (ECM) activates the actuator for the bypass valve during these conditions:
- Turbocharger surge
- Engine shutdown
Turbocharger Surge
A rapid drop in the output power of the generator can cause the engine's speed to quickly increase. The increased speed of the engine causes the turbochargers to overspeed temporarily. This is called a turbocharger surge. Surging can damage the turbochargers.
The ECM continuously monitors the speed of the engine. The ECM responds to a rapid increase in the speed of the engine by activating the actuator for the bypass valve. The actuator opens the valve.
The valve allows the compressed air/fuel mixture in the aftercooler's inlet to flow into the intake of the turbocharger's compressor. This reduces the boost pressure in the air inlet manifold.
Engine Shutdown
Engine shutdown occurs when the output for the fuel control relay is OFF and the engine RPM is above 100. The ECM activates the actuator for the bypass valve until the engine RPM drops to zero. This scavenges any unburned gases in the components of the system during engine shutdown.
CAN Data Link
The ECM and the actuator communicate via the CAN data link. The ECM sends a command signal to the actuator. The actuator sends the following information to the ECM: actuator position, CCM heartbeat, software version, and internal fault diagnosis.
If the ECM cannot communicate with the actuator, the ECM activates a 1720-9 diagnostic code and the engine is shutdown. A 1720-9 diagnostic code is probably caused by a problem with an electrical connector or a harness. The next likely cause is a problem with the actuator. The least likely cause is a problem with the ECM.
Terminating resistors must be connected to each end of the CAN data link. The terminating resistors improve the communication between the devices. If there is an intermittent diagnostic code for any of the devices that are connected to the CAN data link, be sure to check the terminating resistor that is inside the terminal box. Also check the jumper wire that is connected between terminals "J" and "K" on the actuator for the bypass valve. Make repairs, when possible. Replace parts, if necessary.
Identification on the CAN Data Link
When the actuator for the bypass valve is powered up, the actuator looks for a ground on terminal "N". If there is a ground on terminal "N", the actuator will have a unique identification on the CAN data link.
If there is no ground on terminal "N" and the actuator is powered up, the actuator for the bypass valve and the throttle actuator will have the same identification. The ECM will not communicate with the actuator for the bypass valve. Instead, the ECM will activate a 1720-9 diagnostic code. The engine will not start.
The electrical connector for the actuator is designed so that the terminals for electrical power are connected before terminal "N". For this reason, electrical power must be removed before the connector for the actuator is connected.
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| Illustration 1 | g06203138 |
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Schematic for the circuit of the actuator for the bypass valve | |
Test Step 1. Inspect the Electrical Connectors and Wiring
- Remove the electrical power from the engine.
Note: For the following steps, refer to Troubleshooting, "Electrical Connectors - Inspect".
- Thoroughly inspect each of the following connectors:
- J1/P1 connectors
- J9/P9 connectors
- Connectors on the actuator for the bypass valve
- Check the torque of the allen head screw for the ECM connectors.
- Perform a
45 N (10 lb) pull test on each of the wires that are associated with the actuator for the bypass valve.Show/hide table
Illustration 2 g00935459 Right side views - Check the wiring for abrasion and for pinch points from the actuator for the bypass valve to the ECM.
Expected Result:
All of the connectors, pins, and sockets are connected properly. The connectors and the wiring do not have corrosion, abrasion, or pinch points.
Results:
- OK - The components are in good condition with proper connections. Proceed to Test Step 2.
- Not OK - The components are not in good condition and/or at least one connection is improper.
Repair: Perform the necessary repairs and/or replace parts, if necessary. Ensure that all the seals are properly installed. Ensure that the connectors are properly engaged. Verify that the repair has eliminated the original problem.
STOP
Test Step 2. Check for a Diagnostic Code
- Connect the Caterpillar Electronic Technician (ET) to the service tool connector.
- Switch the 35 amp circuit breaker ON. Set the engine control to the STOP mode.
- Use Cat ET to determine if one of the following diagnostic codes is active:
- 1720-9 Turbocharger Compressor Bypass Valve Actuator : Abnormal Update Rate
- 1720-11 Turbocharger Compressor Bypass Valve Actuator invalid
- 1720-12 Turbocharger Compressor Bypass Valve Actuator : Failure
Expected Result:
None of the diagnostic codes are active.
Results:
- OK - None of the diagnostic codes are active. The communication between the ECM and the actuator for the bypass valve appears to be OK at this time. However, diagnostic codes may be logged.
Repair: If you are troubleshooting an intermittent problem, refer to Troubleshooting, "Electrical Connectors - Inspect".
Terminating resistors must be connected to each end of the CAN data link. The terminating resistors improve the communication between the devices. If there is an intermittent diagnostic code for any of the devices that are connected to the CAN data link, be sure to check the terminating resistor that is inside the terminal box. Also check the jumper wire that is connected between terminals "J" and "K" on the actuator for the bypass valve. Make repairs, when possible. Replace parts, if necessary.
STOP
- Not OK (Active 1720-9) - The ECM has detected a problem with the communication between the ECM and the actuator for the bypass valve. Proceed to Test Step 3.
- Not OK (Active 1720-11) - There is an active 1720-11 diagnostic code. This code indicates a problem with the movement of the actuator for the compressor bypass.
Repair: The actuator for the compressor bypass valve must be installed properly to provide stable operation. If the motion is sticky and/or rough, investigate the cause of the binding. Perform the necessary repairs.
STOP
- Not OK (Active 1720-12) - There is an active 1720-12 diagnostic code.
Repair: The actuator for the bypass valve has detected an internal fault. Replace the actuator. Verify that the repair has eliminated the original problem.
STOP
Test Step 3. Check for Electrical Power at the Actuator
- Refer to Illustration 3. Measure the voltage at the junction box.
- Disconnect the electrical connector from the actuator.
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Illustration 4 g01233703 Locations for the voltage check at the harness connector - Measure the voltage between terminals "N" and "P" at the harness connector.
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| Illustration 3 | g01234707 |
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Locations for the voltage check at the junction box | |
Expected Result:
The voltage at the harness connector is within two volts of the voltage at the junction box.
Results:
- Yes - The voltage at the harness connector is within two volts of the voltage at the junction box. The actuator is receiving the proper operating voltage. Proceed to Test Step 4.
- No - The voltage at the harness connector is not within two volts of the voltage at the junction box. The actuator is not receiving the proper operating voltage.
Repair: Determine the cause of the excessive voltage drop. Make the necessary repairs.
STOP
Test Step 4. Check the CAN Data Link for Continuity Between the Actuator for the Bypass Valve and the ECM
- Set the engine control to the OFF/RESET mode. Switch the 35 amp circuit breaker OFF.
- Disconnect the P1 connector. Disconnect the connector for the actuator for the bypass valve.
- Use a multimeter to check for continuity between the points that are listed in Table 1. During each measurement, wiggle the harnesses to check for an intermittent problem with the harness. Be sure to wiggle the harness near each of the connectors. Be sure to wiggle the harness near the fuel metering valve and the throttle actuator.
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Table 1 Points to Check for Continuity Connector and Terminal Harness Connector for the Actuator for the Bypass Valve P1-34 Terminal "B" (CAN data link −) P1-50 Terminal "A" (CAN data link +) P1-42 Terminal "M" (CAN shield)
Expected Result:
The continuity of the circuits between the terminals is good.
Results:
- OK - The continuity of the circuits between the terminals is good. Proceed to Test Step 5.
- Not OK - At least one of the continuity checks indicates an open circuit. There is an open circuit for the CAN data link between the actuator for the bypass valve and the ECM.
Repair: The open circuit could be caused by a poor electrical connection in a connector. Alternatively, the open circuit could be caused by one of the following components:
- The harness inside the terminal box
- The harness between the terminal box and the fuel metering valve
- The harness between the fuel metering valve and the throttle actuator
- The harness between the throttle actuator and the actuator for the bypass valve
- The fuel metering valve
- The throttle actuator
STOP
Test Step 5. Check the CAN Data Link for a Short Circuit
- Verify that the engine control is in the OFF/RESET mode and that the 35 amp circuit breaker is OFF.
- Use a multimeter to check for continuity between the points that are listed in Table 2. During each measurement, wiggle the harnesses to check for an intermittent problem with the harness. Be sure to wiggle the harness near each of the connectors. Be sure to wiggle the harness near the fuel metering valve and the throttle actuator.
Show/hide table
Table 2 Points to Check for Continuity Connector and Terminal Connector and Terminal P1-34 (CAN data link −) P1-50 (CAN data link +)
P1-42 (CAN shield)
P1-52 (+ Battery)
Ground strap for the ECMP1-50 (CAN data link +) P1-42 (CAN shield)
P1-52 (+ Battery)
Ground strap for the ECMP1-42 (CAN shield) P1-52 (+ Battery)
Ground strap for the ECM
Expected Result:
All the measurements indicate an open circuit.
Results:
- OK - All of the measurements indicate an open circuit. The CAN data link does not have a short circuit.
Repair: Connect the P1 connector. Connect the connector for the actuator for the bypass valve.
Proceed to Test Step 6.
- Not OK - At least one of the measurements indicate a short circuit.
Repair: The short circuit could be caused by a poor electrical connection in a connector. Alternatively, the short circuit could be caused by one of the following components:
- The harness inside the terminal box
- The harness between the terminal box and the fuel metering valve
- The harness between the fuel metering valve and the throttle actuator
- The harness between the throttle actuator and the actuator for the bypass valve
- The fuel metering valve
- The throttle actuator
STOP
Test Step 6. Check for a Diagnostic Code
- Switch the 35 amp circuit breaker ON. Set the engine control to the STOP mode.
- Use Cat ET to determine if a 1720-9 diagnostic code is active.
Expected Result:
The 1720-9 code is not active.
Results:
- OK - The 1720-9 code is not active. The problem seems to be resolved. The initial diagnostic code was probably caused by a poor electrical connection.
Repair: If there is an intermittent problem that is causing the code to be logged, refer to Troubleshooting, "Electrical Connectors - Inspect".
STOP
- Not OK - The 1720-9 code is active.
Repair: The active 1720-9 code could be caused by one of the following components:
- The ECM
- The throttle actuator
- The actuator for the bypass valve
- The fuel metering valve
- Temporarily install a new ECM. Refer to Troubleshooting, "ECM - Replace". If the problem is resolved with the new ECM, install the original ECM and verify that the problem returns. If the new ECM operates correctly and the original ECM does not operate correctly, replace the original ECM. Refer to Troubleshooting, "ECM - Replace". If the problem is not resolved with a new ECM, install the original ECM. Continue with this procedure.
- Temporarily install a new actuator for the throttle actuator. If the new throttle actuator operates correctly, the problem is resolved. If the new throttle actuator does not operate correctly, install the original throttle actuator and continue with this procedure.
- Temporarily install a new actuator for the bypass valve. If the new actuator for the bypass valve operates correctly, the problem is resolved. If the new actuator for the bypass valve does not operate correctly, install the original actuator for the bypass valve and continue with this procedure.
- Temporarily install a new fuel metering valve. If the new fuel metering valve operates correctly, the problem is resolved. If the new fuel metering valve does not operate correctly, install the original fuel metering valve. Refer to Troubleshooting, "Electrical Connectors - Inspect".
STOP